UNIVERSITY  OF  CALIFORNIA 

COLLEGE   OF   AGRICULTURE 

AGRICULTURAL    EXPERIMENT   STATION 

CIRCULAR  No.  273 


Saving  the  Gophered  Citrus  Tree 


By  ROBERT  W.  HODGSON 


A  successful  case  of  citrus  inarching. 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


CONTENTS 

PAGE 

Introduction 2 

Methods  of  Treatment 3 

Promoting  Natural  Recovery 3 

Bark  Regeneration 3 

Disinfectants  and  Treatment 4 

Bridge-Grafting 4 

Limitations 4 

The  Operation 4 

Modified  Method 6 

Shoot-bridging 7 

Root-bridging 7 

Inarching 8 

Function  and  Application 10 

The  Standard  Method 10 

Modified  Method 15 

Kind  of  Seedlings 15 

Pruning  Treatment. 16 

Frost  Protection 17 

Cost  of  Treatment 17 

Other  Uses  of  Bridge-Grafting  and  Inarching 18 

Bibliography 18 


INTRODUCTION 

The  pocket  gopher  is  by  far  the  most  destructive  rodent  pest  of 
citrus  trees  in  California,  the  damage  to  trees  and  loss  of  crop  result- 
ing from  its  activity  annually  amounting  to  several  hundred  thousands 
of  dollars.  The  injury  is  produced  by  gnawing  away  the  bark  on  the 
crown  roots  and  the  lower  portion  of  the  trunk,  partially  or  entirely 
destroying  the  means  of  transferring  the  elaborated  foodstuffs  from 
the  leaves  to  the  roots,  which  results  in  the  decline  and,  in  some  cases, 
the  death  of  the  tree.  Few  growers  appreciate  the  full  extent  of  the 
damage  caused  by  the  gopher  for  the  reason  that  its  activity  is  unseen 
and  frequently  never  suspected.  In  the  majority  of  cases  its  work 
is  not  detected  until  months  after  the  injury  is  done,  when  visible 
indications  of  decline  become  evident  in  the  appearance  of  the  trees. 
The  insidious  and  serious  character  of  this  pest  may  be  indicated  by 
the  fact  that  the  work  of  a  single  gopher  in  one  night  may  result  in 
serious  damage  to  six  or  eight  trees. 


Circular  273]  SAVING  THE  GOPHERED  CITRUS  TREE  3 

The  hidden  character  of  its  operations  and  the  difficulties  of  secur- 
ing the  community  cooperation  necessary  for  a  successful  campaign 
of  eradication  render  it  highly  improbable  that  the  California  citrus 
grower  will  ever  be  freed  from  the  ravages  of  the  gopher,  although 
entirely  satisfactory  control  measures  have  been  developed.1  The 
importance  of  every  citrus  grower  being  acquainted  with  methods  of 
treatment  calculated  to  aid  damaged  trees  and  of  knowing  how  to 
apply  them  is,  therefore,  apparent. 

METHODS    OF    TREATMENT 

Since  the  effect  of  gopher  injury  is  to  destroy  or  restrict  the  down- 
ward circulation  of  elaborated  foodstuffs  to  the  roots,  the  problem  is 
to  reestablish  the  bark  connection,  immediately,  either  by  means  of 
bridge-grafting  or  inarching,  or  eventually,  by  encouraging  the  regen- 
eration of  new  bark  tissue.  The  latter  frequently  involves  supple- 
menting the  nutritional  functions  of  the  tree  either  temporarily  or 
permanently  by  means  of  inarching  young  seedlings  to  the  trunk. 

The  effectiveness  and  the  character  of  the  method  of  treatment  are 
determined  by  the  location  of  the  injury,  its  extent,  and  the  time 
elapsed  since  it  occurred.  Obviously  these  can  be  determined  only 
by  careful  examination  of  the  trunk  and  crown  roots.  The  importance 
of  immediate  inspection  and  treatment  cannot  be  overemphasized, 
since  to  delay  treatment  not  only  means  prolonging  the  time  of  recov- 
ery, but  also  materially  reduces  the  probability  of  complete  cure.2 
Earliness  in  treatment  is  without  doubt  the  most  important  factor 
in  determining  success  or  failure. 

PROMOTING  NATURAL  RECOVERY 

Bark  Regeneration. — The  well  known  facts  that  trees  injured 
by  gophers  frequently  recover  without  treatment,  and  that  certain 
methods  of  treatment  serve  to  promote  recovery,  are  based  on  the 
regeneration  of  bark  over  the  injured  areas  from  the  bits  of  live 
cambium  tissue  left.  Certain  environmental  conditions  apparently 
stimulate  bark  regeneration,  and  natural  recovery,  partial  or  com- 
plete, occurs  where  these  factors  are  favorable.     Methods  of  treat- 


i  A  comprehensive  discussion  of  methods  of  control  of  the  pocket  gopher  in 
California,  is  given  by  Joseph  Dixon  in  California  Agricultural  Experiment  Station 
Bulletin  340,  1922. 

2  For  a  discussion  of  methods  of  tree  inspection  as  related  to  orchard  efficiency 
see  California  Agricultural  Experiment  Station  Circular  266,  1923,  by  Robert 
W.  Hodgson. 


4  UNIVERSITY    OF   CALIFORNIA — EXPERIMENT    STATION 

ment  should  therefore  be  designed  to  provide  the  injured  parts  with 
conditions  tending  to  promote  bark  regeneration.  That  growers  have 
long  recognized  this  fact  is  reflected  by  the  more  or  less  common 
practice  of  binding  up  gopher  injuries  with  manure  or  mud  poultices, 
or  of  keeping  damp  soil  about  the  injured  area.  Little  exact  infor- 
mation is  available  concerning  the  factors  conducive  to  bark  regener- 
ation. 

Disinfectants  and  Treatment. — Ample  observational  evidence  is 
at  hand  to  indicate  that  the  application  of  standard  disinfectants  such 
as  corrosive  sublimate,  bordeaux  wash  or  paste,  and  carbolineum  to 
areas  gnawed  by  gophers,  and  especially  to  fresh  injuries,  is  not  to 
be  advised  since  these  apparently  discourage  bark  regeneration.  On 
the  other  hand  the  use  of  warm  grafting  wax,  certain  types  of 
asphaltum  compounds,  and  even  thick  lead  paint,  has  repeatedly  been 
noted  to  stimulate  the  regenerative  process,  especially  in  the  heavier 
soil  types. 

It  is  recommended  in  all  cases  of  recent  injury  that  the  soil  be 
removed  from  the  trunk  and  crown  roots  and  the  injured  areas  be 
thoroughly  coated  with  warm  grafting  wax  or  asphaltum  paint.  It 
must  be  remembered,  however,  that  the  regenerating  cambium  tissue 
is  easily  injured  and  dressings  must  not  be  applied  too  hot,  nor  should 
they  contain  any  penetrating  or  caustic  substances.  Such  treatment 
appears  to  be  more  important  in  soils  of  the  heavier  types  than  in  the 
lighter  soils  where  conditions  are  more  favorable  to  natural  recovery. 

BRIDGE-GRAFTING 

Limitations.^-'Wh.ere  the  injury  is  confined  largely  to  the  trunk 
and  the  problem  is  that  of  reestablishing  bark  connection  with  a 
practically  sound  root  system,  bridge-grafting  may  be  used  with  ad- 
vantage (fig.  1).  The  use  of  this  method,  however,  requires  the  pres- 
ence of  sound  bark  on  the  trunk  below  the  injured  area. 

The  Operation. — The  method  most  commonly  used  is  that  of 
bridging  the  girdled  or  injured  area  with  sour  orange  shoots,  %  to 
%  inch  in  diameter,  spaced  from  1%  to  3  inches  apart  and  inserted 
in  the  bark  above  by  means  of  an  inverted  T  shaped  (X)  incision 
and  below  through  the  ordinary  T-shaped  cut  used  for  budding. 

The  shoots  should  be  cut  slightly  longer  than  the  distance  between 
the  points  of  insertion  above  and  below  in  order  that  when  in  place 
they  will  form  a  slight  arch,  fitting  snugly  against  the  cambium  with 
the  ends  well  under  the  bark.  Before  being  placed  in  position,  the 
shoots  should  be  beveled  at  each  end  with  both  beveled  surfaces  on  the 


Circular  273] 


SAVING  THE  GOPHERED  CITRUS  TREE 


Fig.  1. — A  successful  case  of  bridge-grafting  resulting  in  the  saving  of  a  tree, 
the  bark  on  the  trunk  of  which  was  destroyed  by  disease.  In  cases  of  gopher 
injury  the  areas  bridged  are  usually  much  shorter  and  located  lower  down  on  the 
trunk,  in  many  cases,  partially  underground. 


b  UNIVERSITY    OF   CALIFORNIA — EXPERIMENT    STATION 

same  side.  The  beveling  should  be  done  with  a  long  sloping  cut  so 
that  the  wedge-shaped  ends  will  be  relatively  thin  and  easy  to  insert 
in  place.3 

Although  not  essential  to  success,  it  is  a  distinct  advantage  to  thin 
the  bark  of  the  treated  tree  at  the  points  of  insertion  and  to  fasten 
the  ends  of  the  bridges  in  place  with  small  nails.  On  account  of  the 
danger  of  splitting,  however,  the  nails  should  be  inserted  through 
holes  made  with  a  small  drill  and,  to  avoid  bruising  the  tender  bark, 
should  be  driven  in  place  with  a  nail  set. 

After  insertion,  all  surfaces  as  well  as  the  bridges  themselves, 
should  be  coated  with  warm  grafting  wax  to  prevent  drying.  A  handy 
means  of  treating  the  points  of  insertion  is  to  apply  a  small  rectangu- 
lar shield  of  waxed  cloth  split  at  one  end  in  such  a  manner  as  to  fit 
snugly  against  the  trunk  and  about  the  end  of  the  bridge.  This  forms 
an  effective  weatherproof  covering. 

In  order  to  protect  the  uniting  parts  against  extremes  of  tempera- 
ture and  humidity  it  is  usually  desirable  to  place  damp  soil  over  the 
bridged  area,  forming  a  conical  mound  a  foot  or  more  in  height  about 
the  trunk  of  the  tree.  This  is  left  for  a  month  or  six  weeks  until  union 
has  occurred,  when  it  should  be  removed,  and  the  waxed  cloth  shields 
pulled  off.  If  the  bridging  extends  high  up  on  the  trunk,  burlap 
wrapped  loosely  about  the  trunk  is  generally  used  as  a  means  of 
protection  against  sunburn. 

Bridge-grafting  may  be  done  whenever  the  sap  flow  is  sufficient 
to  permit  of  lifting  of  the  bark.  In  southern  California  this  con- 
dition obtains  practically  the  year  round. 

Modified  Method. — A  modification  of  the  method  above  described 
for  inserting  the  bridges  has  been  successfully  used  in  southern  Cali- 
fornia for  some  years.  Instead  of  using  T-shaped  cuts  for  inserting 
the  ends  of  the  bridges,  strips  of  bark  the  width  of  the  shoots  used 
for  bridging  and  four  to  six  inches  long  are  removed  both  above 
and  below  the  injured  area.  A  loose  flap  of  bark  an  inch  or  so  in 
length  is  left  attached  at  the  upper  end  of  the  strip  above  the  zone 


3  In  bridge-grafting  deciduous  fruit  trees  in  early  spring  before  the  bark  will 
slip,  it  is  necessary  to  make  cuts  for  receiving  the  ends  of  the  scions  rather  than 
trying  to  force  them  under  the  bark.  For  this  purpose  a  short,  quarter-inch  chisel 
which  has  been  ground  down  thin  is  a  convenient  tool.  If  the  tool  is  driven  into 
the  wood  for  half  an  inch  at  the  proper  angle,  the  scions  will  always  remain  per- 
fectly in  place. 

Even  after  the  sap  is  flowing  it  is  often  impracticable  to  insert  the  scions 
beneath  the  bark  especially  when  working  among  the  crown  roots.  Under  such 
conditions  this  method  of  inserting  the  scions  is  recommended.  It  also  has  the 
further  advantage  that  in  its  use  even  an  amateur  cannot  fail  of  having  the 
cambium  surfaces  in  contact  with  each  other. 


Circular  273]  SAVING  THE  GOPHERED  CITRUS  TREE  7 

of  injury  and  at  the  lower  end  of  the  strip  below.  Long  bridges  are 
used  and  these  are  cut  an  inch  or  two  longer  than  the  distance  between 
the  ends  of  the  strips  of  bark  removed. 

The  bridges  are  split  so  as  to  fit  into  the  strips  from  which  the 
bark  has  been  removed,  and  the  ends  beveled  to  a  thin  edge  so  as 
to  fit  snugly  under  the  flaps  of  bark.  The  bridges  are  then  inserted 
and  fastened  in  place  by  means  of  small  nails  or  brads.  After  a  coat 
of  warm  grafting  wax  is  applied,  strips  of  waxed  cloth  are  laid  over 
the  sections  where  the  bark  was  removed  extending  over  the  bark  flaps 
above  and  below,  and  are  securely  held  in  place  by  another  coat  of 
wax,  which  fills  in  all  crevices  and  makes  a  weatherproof  covering. 
This  method  is  somewhat  more  complicated  than  the  one  described 
above  and  does  not  appear  to  have  sufficient  advantages  to  warrant 
its  recommendation. 

Shoot-bridging. — Still  another  modification  is  that  of  selecting 
shoots  produced  from  the  bark  below  the  injured  area  and  when  these 
are  large  enough,  cutting  them  back  to  the  proper  length  and  inserting 
the  upper  ends  in  the  bark  above  the  zone  of  injury.  On  account  of 
the  lower  end  of  the  shoot  being  attached,  rendering  manipulation 
rather  difficult,  the  modified  method  of  insertion  described  above  is 
recommended  for  shoot-bridging.  The  advantage  of  having  to  make 
only  one  union  which  this  method  possesses  is  more  than  offset  in  most 
cases,  however,  by  the  delay  in  treatment  necessitated  by  the  time 
required  to  produce  such  shoots  large  enough  for  use. 

Root-bridging. — Root-bridging  has  been  done  to  a  limited  extent 
and  although  sometimes  successful  is  ordinarily  not  recommended  on 
account  of  other  and  more  satisfactory  methods  being  available. 
Bridging  may  be  done  between  roots  and  trunk  although  usually  not 
advised  on  account  of  mechanical  difficulties.4  Scions  containing 
several  buds  may  be  grafted  into  the  bark  of  the  main  roots  and  the 
shoots  produced  from  these  scions  later  used  for  bridging.  Roots 
may  be  dug  out  while  still  attached  and  the  tips  bent  up  and  inserted. 
While  these  methods  are  of  interest,  none  of  them  compares  favorably 
with  inarching  and  hence  they  cannot  be  recommended  for  general 
use. 


4  With  deciduous  fruit  trees  its  use  is  rather  common  by  means  of  the  chisel 
method  previously  referred  to. 


UNIVERSITY    OF   CALIFORNIA — EXPERIMENT    STATION 


INARCHING 

Inarching  as  a  means  of  saving  injured  trees  has  been  known  to 
horticulturists  and  plant  propagators  for  centuries  but  has  been 
employed  only  occasionally  as  a  means  of  assisting  fruit  trees  to 
recover  from  bark  diseases  and  injuries.  It  was  not  until  compara- 
tively recently  that  its  applicability  to  citrus  trees  injured  by  gophers 


Fig.  2. — Two-year-old  inarches  on  badly  injured  orange  tree.  The  injuries  were 
of  long  standing  when  the  inarching  was  done.  The  tree  has  made  a  remarkable 
recovery.  Note  the  size  of  the  inarches  and  the  ridge  of  growth  above  the  one  on 
the  left. 


was  discovered.  Credit  for  the  demonstration  of  this  fact  is  due 
largely  to  W.  M.  Mertz,  formerly  connected  with  the  Citrus  Experi- 
ment Station,  Riverside,  who  in  1919  successfully  treated  some  200 
gophered  lemon  trees  at  Alta  Loma.  It  should  be  stated,  however, 
that  citrus  trees  in  California  had  been  inarched  before  that  time,  but 


Circular  273] 


SAVING  THE  GOPHERED  CITRUS  TREE 


in  a  small  way  only  and  principally  as  an  aid  to  recovery  from  the 
brown  rot  gum  disease.  As  an  evidence  of  the  rapidity  with  which 
this  method  of  treating  gopher-injured  trees  has  come  into  favor,  it 
is  reported  that  during  the  past  three  seasons  one  individual  has 
inserted  approximately  10,000  inarches.  During  this  same  period 
nurserymen  report  the  sale  of  more  than  25,000  sour  orange  seedlings 
presumably  for  inarching  purposes.  At  the  present  time  the  demand 
for  seedlings  suitable  for  use  in  inarching  exceeds  the  supply. 


%E^Jii3S!ffiR 


Fig.  3. — Thinning  the  bark  at  the  point  of  insertion  of  the  inareh  is  an  ;ii  i 
to  the  operation  as  discussed  in  the  text. 

The  inarching  method  of  treatment  appears  to  offer  many  derided 
advantages  over  all  methods  previously  used.  Most  of  the  trees 
treated  by  this  method  have  shown  satisfactory  recovery.  When 
applied  soon  after  injury,  in  nearly  all  cases  the  trees  have  suffered 
no  appreciable  nutritional  disturbance  and  no  diminution  of  crop 
whatever.  Even  in  very  bad  cases  where  months  had  elapsed  since 
the  injury  occurred  and  where  the  trees  had  shown  pronounced  indi- 
cations of  disorder,  they  were  well  on  the  way  to  recovery  within  two 
seasons  after  treatment  (fig.  2).  It  is  recognized,  however,  that  in 
such  cases  recovery  must  necessarily  be  slow  and  in  a  certain  per  cent 
of  cases  so  delayed  as  to  be  commercially  unsatisfactory. 


10 


UNIVERSITY    OF   CALIFORNIA — EXPERIMENT    STATION 


Function  and  Application. — The  function  of  inarching  is  to  sup- 
plement the  nutritional  processes  of  the  tree  either  temporarily,  in 
the  case  of  recent  injury,  while  bark  regeneration  is  taking  place,  or 
permanently,  in  the  case  of  old  injury,  by  substituting  new  and 
actively  functioning  roots  for  those  lost  by  starvation  or  death  follow- 
ing the  severing  of  bark  connection.  Its  use  is  therefore  recommended 
in  all  cases  of  injury,  whether  recent  or  old,  involving  any  consider- 
able area  of  root  bark,  or  trunk  bark  adjacent  to  the  crown  roots. 


Pig.  4. — Showing  the  cut  end  of  the  seedling  tree  (inarch),  ready  for  insertion. 

The  Standard  Method. — As  commonly  used,  this  method  consists 
in  planting  sour  orange  seedlings,  three  to  five  in  number  and  %  inch 
to  one  inch  in  diameter,  around  the  injured  tree,  at  the  same  time 
inserting  the  trunks  of  the  seedlings  into  the  trunk  of  the  tree — as 
low  down  as  is  possible,  by  means  of  inverted  T-shaped  (X)  incisions, 
in  much  the  same  manner  as  described  for  bridge-grafting. 

The  first  step  in  the  operation  is  the  examination  of  the  trunk  and 
crown  roots  to  determine  the  number  and  proper  placement  of  the 
seedlings.    This  may  be  done  conveniently  by  means  of  a  trench  shovel 


Circular  273] 


SAVING  THE  GOPHERED  CITRUS  TREE 


11 


and  a  gardener's  trowel.  The  points  selected  for  the  insertion  of  the 
seedlings  should  be  as  close  to  the  ground  as  is  possible,  and  not  more 
than  two  to  three  inches  above  the  injury  as  there  is  evidence  to  indi- 
cate that  the  lower  down  the  inarch,  the  more  rapid  the  union  and 
development  of  the  seedling. 


Fig-.   5.     Prepared   seedling  pushed   well   into   place. 
Beady  for  nailing-. 


Note    upright    position. 


The  holes  for  the  seedlings  should  then  be  dug  in  such  a  manner 
that  the  seedlings  may  be  planted  close  to  the  trunk  in  a  relatively 
upright  position  so  as  to  avoid  their  being  pulled  loose  later  by  culti- 
vating tools.  The  holes  should  not  be  larger  than  necessary  to 
accommodate  the  roots  of  the  seedlings,  and  should  be  slightly  deeper 
than  required  when  the  seedlings  are  in  final  position,  in  order  to 
permit  of  some  manipulation  in  pushing  the  seedlings  into  place. 


12 


UNIVERSITY    OF   CALIFORNIA EXPERIMENT    STATION 


The  bark  of  the  injured  tree  at  the  points  of  insertion  should  then 
be  thinned  somewhat  either  by  paring  or  by  scraping,  the  latter  being 
conveniently  done  with  the  back  of  the  knife-blade  (fig.  3).  The 
thinning  of  the  bark  accomplishes  several  objects;  it  renders  it  pliable 
so  that  separation  from  the  cambium  does  not  occur  except  in  the 


Fig.  6. — The  cut  end  of  the  seedling  is  fastened  tightly  against  the  cambium 
layer  of  the  tree  by  means  of  a  small  nail  inserted  through  a  previously  drilled 
hole. 


immediate  vicinity  of  the  incisions,  a  matter  of  importance;  and  it 
cleans  the  bark  so  that  dirt  is  not  likely  to  be  smeared  on  the  cut 
surfaces  of  the  seedlings.  Inverted  T-shaped  (X)  incisions  are  then 
made  in  the  back  on  the  thinned  areas,  the  vertical  cut  being  not 
longer  than  1%  to  2  inches  and  the  horizontal  cut  just  long  enough 
to  permit  of  easy  insertion  of  the  cut  ends  of  the  seedlings. 


Circular  273]  SAVING  THE  GOPHERED  CITRUS  TREE  13 

The  seedlings  are  next  shortened  to  approximately  the  correct 
length  and  prepared  for  insertion,  each  being  trimmed  with  a  single 
long  sloping  cut  of  proper  angle  to  provide  for  the  contact  of  con- 
siderable cambium  tissue  and  a  relatively  upright  position  when  in 
place  (fig.  4).  A  slight  arc  to  the  cut  may  be  used  to  insure  good 
cambium  contact  and  it  is  sometimes  desirable  to  trim  the  bark  si  do 
of  the  tips  slightly  to  facilitate  insertion  without  pulling  the  bark 
loose. 

The  corners  of  the  bark  at  the  incisions  are  then  raised  and  the 
seedlings  pushed  into  the  slits  so  that  the  tips  of  the  cut  ends  are 
well  past  the  upper  end  of  the  slit,  and  cambium  contact  is  secured 
all  round  (fig.  5).  Where  the  bark  is  thick  or  the  sap  flow  poor,  n 
sharpened  tooth-brush  handle  or  shoot  taken  from  dormant  growth 
greatly  facilitates  lifting  it  and  assists  in  inserting  the  seedlings. 
When  securely  in  place,  the  cut  surfaces  of  the  seedlings  are  fastened 
tightly  to  the  trunk  of  the  treated  tree  by  means  of  %  to  %  inch  nails 
inserted  one  to  each  seedling  through  a  hole  bored  with  a  small  hand 
drill  or  gimlet  just  before  insertion  (fig.  6).  The  nails  should  be 
driven  in  carefully  and  forced  into  final  position  with  a  nail  set  in 
order  to  avoid  bruising  the  tender  bark,  a  common  cause  of  failure 
after  union  occurs.  The  nails  should  never  be  driven  through  the 
ends  of  the  seedlings  without  holes  having  previously  been  drilled ;  if 
not  done,  splitting  of  the  seedlings  is  likely  to  result. 

Damp  soil  should  then  be  filled  in  and  tamped  about  the  roots, 
taking  special  pains  to  firm  the  soil  about  them  so  as  to  establish  good 
contact  between  soil  and  roots  and  to  prevent  settling  after  irrigation. 

A  good  coating  of  warm  grafting  wax:5  should  now  be  applied  to 
the  points  of  insertion  (fig.  7)  and  as  an  extra  precaution  it  is  some- 
times desirable  to  coat  the  bark  surface  of  the  inarches  as  well,  to 
prevent  excessive  evaporation.  It  is  very  important  not  to  apply  the 
wax  too  hot  as  the  bark  and  cambium  are  easily  injured  by  heat. 
Soft  and  sticky  waxes  are  also  objectionable  as  they  apparently  retard 
healing. 

Although  not  required  for  success.it  is  recommended  that  as  an 
additional  precaution  the  points  of  insertion  be  further  protected  by 


s  Many  formulas  for  making  grafting  wax  are  in  common  use.     Two  of  the 
best  are  as  follows: 

Formula  1.     Melt  together,  taking  care  not  to  allow  to  boil,  one  pound  of  bees- 
wax and  two  pounds  of  rosin. 

Formula  2.     Melt  together  one  pound  of  beeswax,  five  pounds  of  rosiu,  and 
one-half  pound  of  tallow  or  one  pint  of  raw  linseed  oil. 


14 


UNIVERSITY    OF   CALIFORNIA — EXPERIMENT    STATION 


the  application,  while  the  wax  is  still  warm,  of  small  shields  of  waxed 
cloth6  split  at  the  lower  end  so  as  to  fit  tightly  to  the  bark  of  the  tree 
and  snugly  about  the  inserted  ends  of  the  inarches.  The  waxed  cloth 
should  be  held  in  place  by  another  coat  of  warm  wax  (fig.  8). 


Fig.  7. — After  tamping  the  soil  about  the  roots,  the  point  of  insertion  is 
thoroughly  covered  with  warm  grafting  wax. 

A  shallow  basin  should  then  be  constructed  about  the  trunk  of  the 
tree  and  irrigation  water  applied  immediately.  For  some  months 
after  inarching  it  is  desirable  to  water  the  trees  in  this  manner  at 
intervals  of  ten  days  to  two  weeks  in  addition  to  the  usual  orchard 
irrigation  schedule. 


6  Waxed  cloth  for  inarching  may  be  purchased  from  seed  houses,  nurserymen, 
and  budders  but  may  easily  be  made  at  home.  A  fairly  good  grade  of  bleached 
muslin  should  be  used,  such  as  Daisy  or  Hope,  wound  in  six-inch  strips  on  a  stick 
and  thoroughly  soaked  in  a  solution  of  warm  wax  composed  of  one  pound  of 
beeswax  and  five  pounds  of  parowax. 


Circular  273] 


SAVING  THE  GOPHERED  CITRUS  TREE 


15 


As  a  means  of  providing  conditions  of  temperature  and  moisture 
favorable  to  union  it  is  the  common  practice  after  the  first  irrigation 
to  mound  up  damp  soil  about  and  over  the  inarches  and  to  irrigate 
thereafter  in  a  circular  ditch  or  furrow  at  the  base  of  the  mound. 
After  a  month  or  six  weeks  when  union  has  taken  place  the  mounds 
are  pulled  down  and  the  waxed  cloth  shields  removed. 


Fig.  8. — As  an  additional  precaution  a  waxed  cloth  shield  is  used,  held  in  place 
by  another  coat  of  warm  wax. 


Modified  Method. — A  modification  of  the  method  just  described 
has  been  used  successfully  by  L.  H.  Dawson  of  Corona  for  some  years 
and  consists  in  the  removal  of  a  strip  of  bark  leaving  a  flap  at  the 
upper  end  and  splitting  the  seedling  and  nailing  it  in  place  as  de- 
scribed for  the  modified  method  of  bridge-grafting. 

Kind  of  Seedlings. — The  use  of  sour  orange  seedlings  for  inarch- 
ing is  recommended  on  account  of  the  greater  resistance  of  this  variety 


16 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT-  STATION 


to  trunk  and  root  diseases.  It  is  generally  cheaper,  more  satisfactory, 
and  convenient  to  use  seedlings  with  bare  roots  instead  of  balled  seed- 
lings, although  the  latter  may  be  preferable  under  certain  conditions. 
It  is  important,  however,  that  the  seedlings  used  be  vigorous  and 
thrifty  and  not  discarded  stock  unsuitable  for  nursery  trees. 


Fig.  9. — Complete  equipment  need  in  inarching.  The  trench  shovel  and  gar- 
deners' trowel  are  used  in  excavating  about  the  tree  for  examination  and  for 
placement  of  the  inarches.  The  lower  part  of  the  tool  box  contains  the  seedling 
trees  packed  in  sphagnum  moss  and  the  tray  carries  the  brush  for  cleaning  the 
bark,  the  knives,  also  drill,  hammer,  and  nail  set  and  other  tools  frequently  found 
to  be  convenient.  The  wax  is  kept  warm  by  a  one-burner  kerosene  stove  in  the 
five -gallon  oil  can  used  for  heater. 


PRUNING    TREATMENT 

Pruning  treatment  for  gophered  trees  is  determined  by  the  extent 
of  injury,  the  period  elapsed  since  the  injury  occurred,  and  the 
character  of  the  treatment  given.  Even  where  trees  have  been  vir- 
tually girdled,  if  early  treatment  has  been  provided,  little  or  no 
pruning  is  required. 

If  the  injury  is  not  extensive  and  natural  recovery  is  relied  upon, 
a  moderate  thinning  of  the  top  is  desirable  in  order  to  restore  as 
nearly  as  possible  the  balance  between  the  root  system  and  the  parts 
above  ground. 


CIRCULAR  273]  SAVING  THE  GOPHERED  CITRUS  TREE  17 

If  the  injury  is  old,  and  the  appearance  of  the  trees  indicates 
nutritional  disorder,  it  appears  to  be  desirable  to  remove  a  part  of 
the  top.  This  removal  of  parts,  however,  should  be  accomplished  by 
a  thinning  process  rather  than  by  heading  or  ' '  stubbing. ' '  Where  the 
injury  is  extensive  and  the  conditions  of  the  trees  decidedly  weak, 
skeletonizing  may  be  necessary  if  they  are  to  be  saved.  Where  such 
is  the  case,  however,  it  is  questionable  whether  the  trees  are  worth 
saving,  even  though  it  be  possible  to  do  so. 

FROST    PROTECTION 

For  two  or  three  seasons  after  insertion,  bridge-grafts  and  in- 
arches, and  especially  the  thinned  bark  areas  about  the  points  of 
insertion,  are  quite  susceptible  to  injury  from  low  winter  tempera- 
tures. In  districts  where  damaging  frosts  are  likely  to  occur  it  is 
desirable  to  protect  the  treated  trees  against  frost  injury. 

Mounding  dry  soil  around  the  trunks  is  recommended  as  the 
simplest  and  easiest  method  of  affording  satisfactory  protection, 
although  open  to  the  objection  of  increasing  the  danger  of  infection 
with  the  brown  rot  gum  disease.  This  may  be  minimized,  however, 
by  coating  the  lower  parts  of  the  trunks  with  bordeaux  paste  prior  to 
mounding  the  soil  about  them.  The  treated  trees  should  be  provided 
with  suitable  protection  in  late  fall  and  the  mounds  pulled  away  in 
early  spring  as  soon  as  danger  from  frosts  is  past. 

COST    OF   TREATMENT 

The  cost  of  treating  gophered  trees  varies  according  to  the  method 
used,  and  ranges  from  twenty  to  thirty  cents  each  for  slight  injuries, 
to  $1.50  to  $2.00  for  extensive  injuries  that  require  the  use  of  three 
or  four  inarches.  Labor  is  usually  the  principal  factor  in  determin- 
ing the  cost  of  treatment  although  in  the  case  of  inarching  at  the 
present  time  the  cost  of  the  seedlings  used  practically  equals  the  labor 
costs. 

A  statement  of  costs  for  the  present  season  for  a  treatment  requir- 
ing nearly  two  thousand  seedlings  and  extending  over  two  months, 
furnished  by  a  commercial  operator,  is  as  follows : 

1859  sour  orange  seedlings  (in  different  lots)  $435.70 

Average  cost  per  seedling $.235 

Labor  (operator  and  one  assistant)  441.00 

Average  cost  per  seedling .237 

Total  cost  per  seedling  inserted .472 

Average  of  three  seedlings  used  per  tree 3 

Total  average  cost  per  tree  treated $1.42 


18  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


OTHER    USES    OF    BRIDGE-GRAFTING    AND    INARCHING 

The  methods  of  bridge-grafting  and  inarching  described  in  this 
circular  have  already  been  used  in  a  limited  way  in  the  treatment 
of  bark  and  root  injuries  of  other  kinds  and  will  doubtless  receive 
more  extended  use  in  the  future.  Bridge-grafting  has  been  employed 
very  successfully  for  saving  trees  partially  or  entirely  girdled  by 
field  mice  or  the  brown  rot  gum  disease  (fig.  1).  Inarching  has  also 
been  used  with  advantage  in  treating  similar  injuries  as  well  as  for 
the  restoration  of  roots  lost  by  smudge-oil  injury  and  various  forms 
of  fungi  producing  root  decay. 

Inarching  is  now  receiving  considerable  attention  as  a  means  of 
supplementing  the  root  systems  of  stunted  or  declining  trees,  with 
young  and  vigorous  roots  of  more  congenial  stocks,  in  the  hope  that 
thereby  they  may  be  invigorated  or  brought  back  into  productive 
condition.  In  numerous  cases  such  treatment  has  proved  decidedly 
beneficial.  The  inarching  of  citrus  trees  for  this  purpose  has  been 
rather  widely  used  in  Florida  and  with  success.  In  California,  how- 
ever, this  practice  is  at  the  present  time  purely  experimental  and  some 
years  will  be  required  before  its  value  in  such  cases  will  be  definitely 
determined. 

With  slight  modifications  according  to  the  requirements,  all  the 
methods  described  herein  are  applicable  to  the  other  classes  of  fruit 
and  nut  trees  grown  commercially  in  California. 


BIBLIOGRAPHY 

1879.     The  Art  of  Grafting  and  Budding,  by  Charles  Baltet.     English  translation, 

pp.  54  and  213.     Macmillan  and  Company,  London. 
1896.     Methods  of  Propagating  the  Orange  and  Other  Citrus  Fruits,  by  H.  J. 

Webber.     Yearbook,  U.  S.  D.  A.,  pp.  488-489. 
1911.     Citrus  Fruits  and  Their  Culture,  by  H.  H.  Hume,  ed.  4,  p.  196.     Macmillan 

and  Company,  New  York. 
1916.     Bridge-grafting  of  Fruit  Trees,  by  W.  F.  Fletcher.     Farmers'  Bull.  No. 

710,  U.  S.  D.  A.,  pp.  1-8. 

1916.  Inarching  Citrus  Trees,  by  H.  D.  Eundle.     California  Cultivator,  Vol.  46, 

No.  18,  p.  540. 

1917.  Saving  the  Girdled  Fruit  Trees,  by  W.  C.  Gillespie.     Extension  Circular 

No.  54,  Penn.  State  College,  pp.  1-8. 
1919.     Bridge-grafting  on  Citrus,  by  E.  H.  Paddock.     Mo.  Bull.  Calif.  State  Com. 
of  Hort.,  Vol.  8,  No.  2,  pp.  72-73. 


CIRCULAR  273]  SAVING  THE  GOPHERED  CITRUS  TREE  19 

1921.  Saving  the  Gophered   Tree,  by  Eobert  W.   Hodgson.     Calif.   Citrograph, 

Vol.  6,  No.  10,  pp.  352,  353. 

1922.  Improved   Method   of   Inarching   or   Bridge-grafting,   by   C.   S.    Pomeroy. 

Calif.  Cultivator,  Vol.  59,  No.  1,  p.  3. 

1923.  Experiments  in  Bridge  Grafting  and  Inarching  in  Connection  with  Gum- 

mosis  of  Citrus,  by  H.  S.  Fawcett.     Calif.  Citrograph,  Vol.  8,  No.  3, 

pp.  68  and  95. 
1923.     Gum  Diseases  of  Citrus  Trees  in  California,  by  H.  S.  Fawcett.     Bull.  No. 

360,  Calif.  Agr.  Exp.  Station,  p.  390. 
1923.     The  Pruning  of  Citrus  Trees  in  California,  by  Eobert  W.  Hodgson.     Bull. 

No.  363,  Calif.  Agr.  Exp.  Station,  p.  528. 


